1. Field of the Invention
This invention relates to a polyolefin composition. More particularly it relates to a polyolefin composition capable of affording a molded product having a superior resistance to impact-whitening, luster, impact resistance, mechanical strength and stiffness.
2. Description of the Related Art
Propylene polymers generally have superior processability, chemical resistance, electric properties and mechanical properties so that they have been processed into injection-molded product, blow-molded product, film, sheet, fibers, etc. and used for various applications. However, these properties, particularly impact resistance, cannot often be said to be sufficient in various concrete applications; thus there has been raised a problem that it is difficult to use the polymers for molded products to be subjected to mechanical impact or molded products to be used at low temperatures. In general, the stiffness and impact resistance of plastic materials stand in an inconsistent relation to each other. Thus it is very often difficult to improve the former and the latter at the same time. As to improvement in the impact resistance of propylene polymers, various processes have been proposed. For example, a process of blending a low density polyethylene, a high density polyethylene, a non-crystalline ethylene-propylene random copolymer or the like with propylene polymers, followed by subjecting the blend to a melt-kneading treatment and a process of block-copolymerizing propylene with ethylene have been well known. However, ethylene-propylene block copolymers have a notably improved impact resistance as compared with propylene homopolymers, but on the other hand, when the copolymers are subjected to impact by stress, there is a problem that the part onto which the stress has been concentrated becomes white-turbid, that is, it whitens so that the commodity value of molded products obtained therefrom is notably damaged.
Thus, in order to improve the impact resistance and resistance to impact-whitening of propylene polymers, polyolefin compositions obtained by blending a high density polyethylene and a non-crystalline ethylene-propylene random copolymer each in a specified quantity with a propylene polymer (see Japanese patent publication No. Sho 39-18746/1964, Japanese patent publication No. Sho 47-26369/1972, Japanese patent application laid-open No. Sho 48-71478/1973, Japanese patent publication No. Sho 49-15044/1974, Japanese patent application laid-open No. Sho 49-99351/1974 Japanese patent application laid-open No. Sho 53-42234/1978, Japanese patent application laid-open No. Sho 54-41950/1979, Japanese patent application laid-open No. Sho 56-163137/1981, Japanese patent application laid-open No. Sho 58-185634/1983, Japanese patent application laid-open No. Sho 58-208337/1983 and Japanese patent application laid-open No. Sho 60-112844/1985), and in order to improve the impact resistance, resistance to impact-whitening and stiffness of propylene polymers, polyolefin compositions obtained by adding at least one kind of nucleating agents selected from aromatic sulfonic acid compounds and organic carboxylic acid compounds to a ternary component mixture consisting of a propylene polymer, a high density polyethylene and an amorphous ethylene-propylene copolymer (see Japanese patent publication No. Sho 45-23416/1970) have so far been proposed. Further, in order to make the crystallization temperature of propylene polymers close to their melting points, a polyolefin composition has been proposed which is obtained by blending a high density polyethylene or a non-crystalline ethylene-propylene random copolymer with one or two kinds selected from propylene homopolymer, crystalline .alpha.-olefin-propylene random copolymers and crystalline ethylene-propylene block copolymers and having a sodium organophosphate contained in the resulting blend (see Japanese patent application laid-open No. Sho 61-103944/1986).
However, in the case of the above polyolefin compositions obtained by blending a high density polyethylene and a non-crystalline ethylene-propylene random copolymer each in a specified quantity with a propylene polymer, proposed in the above Japanese patent publication Nos. Sho 39-18746/1964 and Sho 47-26369/1972, Japanese patent application laid-open No. Sho 48-71478/1973, Japanese patent publication No. Sho 49-15044/1974, Japanese patent application laid-open Nos. Sho 49-99351/1974, Sho 53-42234/1978, Sho 54-41950/1979, Sho 56-163137/1981, Sho 58-185634/1983, Sho 58-208337/1983 and Sho 60-112844/1985, the impact resistance and resistance to impact-whitening of the compositions have been considerably improved, but the stiffness thereof is still not satisfactory. Further, in the case of polyolefin compositions obtained by adding at least one kind of nucleating agent selected from aromatic sulfonic acid compounds and organic carboxylic acid compounds to a ternary component mixture consisting of a propylene polymer, a high density polyethylene and an amorphous ethylene-propylene copolymer, proposed in the above Japanese patent publication No. Sho 45-23416/1970, the impact resistance and resistance to impact-whitening of the compositions have been considerably improved as in the above case and the improvement effect in the stiffness has been observed to a certain extent, but is still not satisfactory. Further, in the case of the above polyolefin composition obtained by blending a high density polyethylene or a non-crystalline ethylene-propylene random copolymer with at least one kind selected from propylene homopolymer, crystalline .alpha.-olefin propylene random copolymers and crystalline ethylenepropylene block copolymers, and having a sodium organophosphate contained in the resulting blend, proposed in the above Japanese patent application laid-open No. Sho 61-103944/1986, the improvement effect of the stiffness of the composition has been considerably observed due to the blending of the sodium organophosphate, but it has been impossible to satisfy the three properties of impact resistance, resistance to impact-whitening and stiffness at the same time. Further, the just above Japanese patent application laid-open No. Sho 61-103944/1986 does not disclose at all a polyolefin composition obtained by blending a high density polyethylene and a non-crystalline ethylene-propylene random copolymer with propylene homopolymer, a crystalline .alpha.-olefin-propylene random copolymer or a crystalline ethylene-propylene block copolymer as main components and further having a sodium organophosphate contained in the resulting blend, and there is no disclosure therein suggesting that it is possible for the above polyolefin composition to improve at the same time the three properties of impact resistance, resistance to impact-whitening and stiffness.
The present inventors have made extensive research in order to solve the above-mentioned problems relative to the above polyolefin compositions, and as a result have found that the following compositions can solve the above problems:
.circle. a composition obtained by blending a high density ethylene polymer, a non-crystalline ethylene-propylene random copolymer or a non-crystalline ethylene-propylene-non-conjugated diene random copolymer and a phosphate compound expressed by the following formula (I) (hereinafter referred to as "compound (a)"): ##STR2## wherein R.sub.1 represents sulfur or an alkylidene group of 1 to 4 carbon atoms; R.sub.2 and R.sub.3 each represent a hydrogen atom or the same or different alkyl groups of 1 to 8 carbon atoms; M represents a monovalent, divalent or trivalent metal atom; m represents 0 or 1; and n represents an integer of 1 to 3, with a crystalline .alpha.-olefin-propylene random copolymer, in specified proportions, respectively;
.circle. a composition obtained by blending a high density ethylene polymer, a non-crystalline ethylene-propylene random copolymer or a non-crystalline ethylene-propylene-non-conjugated diene random copolymer and the above compound (a), with a crystalline .alpha.-olefin-propylene random copolymer and a propylene homopolymer, in specified proportions, respectively; and (3) a composition obtained by blending a high density ethylene polymer, a non-crystalline ethylene-propylene random copolymer or a non-crystalline ethylene-propylene-non-conjugated diene random copolymer and the above compound (a), with a crystalline .alpha.-olefin-propylene random copolymer and a crystalline propylene homopolymer having a specified isotactic pentad ratio, in specified proportions, respectively, these compositions further being able to afford molded products having superior luster and mechanical strength.